﻿DEVELOPMENT 
  OF 
  CALOPTENUS 
  ATLANIS. 
  275 
  

  

  the 
  cellular 
  wall 
  of 
  the 
  heart 
  itself, 
  l^o 
  nuclei 
  could 
  be 
  detected 
  among 
  

   these 
  granules. 
  

  

  The 
  trachece. 
  — 
  The 
  tracheal 
  system 
  at 
  this 
  period 
  could 
  not 
  with 
  cer- 
  

   tainty 
  be 
  made 
  out 
  in 
  our 
  sections, 
  although, 
  as 
  will 
  be 
  seen, 
  the 
  urinary 
  

   or 
  Malpighian 
  tubes 
  are 
  clearly 
  indicated. 
  Only 
  two 
  or 
  three 
  sections 
  

   (Fig. 
  3 
  tr) 
  show 
  clearly 
  what, 
  judging 
  from 
  Hatschek's 
  figures, 
  we 
  sup- 
  

   pose 
  to 
  be 
  a 
  section 
  of 
  a 
  main 
  tracheal 
  tube. 
  This 
  section 
  is 
  evidently 
  

   through 
  one 
  of 
  the 
  anterior 
  segments 
  of 
  the 
  thorax 
  as 
  it 
  passes 
  through 
  a 
  

   pair 
  of 
  legs 
  (I). 
  But 
  in 
  the 
  sections 
  posterior 
  to 
  this, 
  especially 
  the 
  ab- 
  

   dominal 
  one, 
  the 
  organ 
  which 
  we 
  judge 
  to 
  be 
  the 
  trachea 
  does 
  not 
  reap- 
  

   pear, 
  nor 
  are 
  there 
  any 
  indications 
  of 
  sections 
  of 
  smaller 
  tracheal 
  tubes 
  

   to 
  be 
  found, 
  unless 
  the 
  circle 
  of 
  cells 
  in 
  the 
  section 
  of 
  the 
  leg 
  (Fig. 
  3, 
  tr 
  f) 
  

   be 
  such, 
  though 
  the 
  preparations 
  are 
  good 
  enough 
  to 
  show 
  them 
  if 
  they 
  

   were 
  present. 
  The 
  body 
  or 
  organ 
  which 
  I 
  provisionally 
  regard 
  as 
  the 
  

   first 
  indication 
  of 
  the 
  main 
  lateral 
  trachea 
  (Fig. 
  3 
  tr 
  and 
  3 
  a) 
  lies 
  out- 
  

   side 
  of 
  the 
  yolk, 
  and 
  is 
  clearly 
  the 
  result 
  of 
  an 
  invagination 
  of 
  the 
  ecto- 
  

   blast. 
  It 
  is 
  situated 
  directly 
  above 
  the 
  insertion 
  of 
  the 
  limb 
  (Z), 
  at 
  the 
  

   place 
  where 
  we 
  should 
  naturally 
  look 
  for 
  the 
  first 
  indications 
  of 
  the 
  

   trachea. 
  Its 
  structure 
  at 
  this 
  period, 
  as 
  seen 
  in 
  Fig. 
  3^, 
  is 
  nearly 
  the 
  

   same 
  as 
  in 
  the 
  Lepidoptera 
  (compare 
  Hatschek's 
  Taf. 
  II, 
  Fig. 
  3 
  tr), 
  there 
  

   being 
  an 
  outer 
  layer 
  of 
  cylindrical 
  epithelium, 
  with 
  often 
  large 
  nuclei, 
  

   "while 
  the 
  cylindrical 
  cells 
  are 
  replaced 
  by 
  an 
  inner 
  mass 
  of 
  polygonal 
  

   cells. 
  

  

  The 
  digestive 
  canal. 
  — 
  A.t 
  this 
  period 
  the 
  two 
  extremities 
  of 
  the 
  digest- 
  

   ive 
  canal 
  have 
  been 
  formed 
  by 
  the 
  infolding 
  or 
  invagination 
  of 
  the 
  ecto- 
  

   blast 
  (epiblast). 
  It 
  will 
  be 
  remembered 
  that 
  the 
  first 
  section 
  of 
  the 
  canal, 
  

   which 
  becomes 
  in 
  the 
  adult 
  the 
  mouth, 
  oesophagus 
  and 
  crop, 
  is 
  in 
  the 
  

   embryo 
  called 
  the 
  stomodceum 
  ; 
  and 
  the 
  third 
  section, 
  corresponding 
  to 
  

   the 
  rectum 
  and 
  intestine, 
  is 
  called 
  the 
  proctodwum. 
  In 
  the 
  first 
  section 
  

   through 
  the 
  brain 
  and 
  eyes 
  the 
  microtome 
  i3assed 
  through 
  a 
  portion 
  of 
  

   the 
  stomodceum. 
  It 
  is 
  seen 
  to 
  be 
  composed 
  of 
  the 
  usual 
  two 
  sub-layers, 
  

   the 
  inner 
  or 
  glandular 
  (Darmdrusenlage) 
  and 
  the 
  outer 
  (Darmfaserlage) 
  

   or 
  fibrous 
  layer. 
  

  

  Turning 
  now 
  to 
  the 
  proctodwum 
  (compare 
  PI. 
  XXI, 
  Fig. 
  8, 
  8a), 
  showing 
  

   the 
  first 
  and 
  third 
  sections 
  of 
  the 
  digestive 
  tract 
  at 
  a 
  little 
  later 
  stdge, 
  

   while 
  the 
  middle 
  section 
  or 
  future 
  stomach 
  (mesenteron) 
  is 
  undeveloped), 
  

   Figs. 
  6-9 
  represent 
  diiferent 
  sections 
  through 
  the 
  proctodseum, 
  which 
  is 
  a 
  

   short 
  thick 
  tube, 
  with 
  the 
  glandular 
  and 
  fibrous 
  layer 
  already 
  developed. 
  

   Fig. 
  6 
  passes 
  through 
  the 
  anterior 
  end, 
  and 
  Fig. 
  8 
  through 
  the 
  rectum 
  and 
  

   anus. 
  Fig. 
  8 
  shows 
  clearly 
  the 
  primitive 
  opening 
  into 
  the 
  rectum, 
  the 
  

   ectoblast 
  having 
  grown 
  or 
  pushed 
  in 
  from 
  the 
  hinder 
  end 
  of 
  the 
  blasto- 
  

   derm, 
  the 
  ends 
  of 
  which 
  are 
  cut 
  through, 
  as 
  seen 
  in 
  Figs. 
  7, 
  8, 
  8 
  a, 
  9 
  bl. 
  

   The 
  glandular 
  layer, 
  composed 
  of 
  columnar 
  epithelium, 
  is 
  seen 
  to 
  be 
  

   completely 
  formed, 
  while 
  the 
  polygonal 
  cells 
  of 
  the 
  fibrous 
  layer 
  are 
  seen 
  

   to 
  be 
  splitting 
  off 
  or 
  separating 
  from 
  the 
  original 
  ectodermal 
  layer. 
  The 
  

   latter 
  is 
  seen 
  to 
  be 
  continuous 
  with 
  the 
  amnion 
  {am) 
  j 
  the 
  double 
  rows 
  of 
  

  

  